Nick,
Nice synopsis - for both experienced and non-experience I would
think.
Thanks
Gary
From: [email protected] [mailto:[email protected]] On Behalf Of Nick
Williams
Sent: Wednesday, April 19, 2006 1:24 PM
To: [email protected]
Cc: John Woodgate
Subject: Re: Electrical safety of machines
I hear the argument you are making, John, but with the benefit of
about ten years of experience dealing with the Machinery Directive
I'm rather more positive about its approach. Since I believe the
approach which the new LVD will take (when it finally get enacted)
will be modelled on the Machinery Directive, I think it's worth
spending a little time looking at this in more detail.
What the LVD does at present is it says "Here's a set of VERY basic
safety objectives and here's a list of standards. If you apply these
standards, you will (probably) meet the very basic safety objectives,
and at very least you will have some evidence that you tried to meet
the safety objectives even if you are ultimately found to have
failed. Either way, you will be able to CE mark your product and sell
it anywhere in Europe without having to meet any additional rules".
What the Machinery Directive says is "Here's a detailed list of basic
safety objectives. You HAVE to meet these except where they patently
do not apply to your machine. If you want a yard stick against which
to measure whether or not you have meet the safety objectives which
apply to your machine, here's a list of standards you can use. Some
of these standards are general, some of them are specific, but they
all support one or more of the basic safety objectives of the
Directive. If you use them you will (probably) meet the basic safety
objectives, and at very least you will have some evidence that you
tried to meet the safety objectives even if you are ultimately found
to have failed. Either way, you will be able to CE mark your product
and sell it anywhere in Europe without having to meet any additional
rules".
Superficially the approaches look very similar, but they are subtly
different and, so far as the standards are concerned, the differences
are immense.
LVD standards are essentially comprehensive. In general, you need
only apply one standard and it covers all of the hazards associated
with a piece of equipment (OK, so where a standard has a General and
a Particular requirement, you need two documents, but in theory at
least they come together to make a single standard).
Machinery standards are very different. The most important ones are
called 'type B' standards and usually cover only one aspect of a
machine's design. For example, EN 418 deals with emergency stops, EN
1037 tells you how to ensure energy sources are isolated, EN 999
tells you how to use light guards, EN 982 gives rules for the use of
hydraulics, etc etc. There are maybe 100 or 200 of these 'type B'
standards. Some machines will have only a few which apply, others
will have many, but they are all oriented around providing guidance
on the design of a particular aspect of machinery in general, rather
than dealing the the overall design of a specific type of machinery.
There are also hundreds of standards (so called 'type C' standards)
which deal with specific types of machinery. For example, EN 693
deals with hydraulic power presses, EN 1494 deals with vehicle jacks
and EN 201 is the standard for injection moulding machines. These
standards contain lots of specific requirements for the types of
machinery which they cover, but they also contain a lot of references
to the 'type B' standards, and they may say things like "clause
1.2.3.4 of EN 123 does not apply to horizontal light curtains used on
power presses with closing speed of less than 30mm/second". There are
no type C standards which are self contained - i.e. which can be used
without any reference to the type B standards.
So, whenever one applies standards in support of the Machinery
Directive, one is always going to have to pick and choose which parts
of which standard to apply. This might not suit those of a nervous
disposition who want everything laid out in black and white, but for
more adventurous souls, who are prepared to get a grip on the process
and use it to their advantage, it provides immense flexibility in how
the standards are applied.
The reasons for this are obvious. The scope of the Machinery
Directive is so broad that it would be quite simply impossible to
create type C standards for every different type of machine. One
might argue, with some merit, that the scope of the LVD is no less
broad in its own way, but I think an analysis will show that the
hazards which are contained in most electrical equipment are of a
lesser range than those in machinery.
I have to say that the Machinery Directive approach provides a lot
more exposure to poor standards writing since particularly the type
'c' standards committees are often populated by people with a
particular axe to grind, and with too few others to be able to
balance their position. I've certainly concluded that one should not
necessarily believe everything which one reads in a type C standard.
However, the Directive is very clear that you do not necessarily need
to comply with the requirements of a standard, but if you do not you
will need to justify in your Technical File how it is that what you
have done as an alternative is adequate. The same possibility exists
within the LVD of course, but it seems to me that lot's a lot less
well understood or used.
Overall, you really can't escape from the need for experience and
expertise if you are going to successfully comply with either
directive, and I realise that's not much comfort to people who are at
the bottom of the learning curve. It's true of any engineering
problem though (and it keeps people like me in work!).
I'd also observe that the Machinery approach to standards is already
starting to creep into LVD compliance. EN 50366 is a case in point -
it's a standard which is focused on a particular type of hazard
rather than on a particular type of equipment. Likewise, for anything
with a laser in it, the LVD standard will probably refer to EN 60825
rather than trying to give detailed requirements for laser safety.
The new LVD looks a lot more like the Machinery Directive, in that it
has a much expanded set of essential requirements. I doubt we will
ever see a wholesale re-write of all the electrical equipment safety
standards to create a three tier structure such as the type A, B and
C machinery standards, but I think we will see more new standards
which deal with particular hazards rather than standards which deal
with particular groups of equipment.
Sory if this is rather long winded and boring, but it seemed to me it
was worth putting on the record for those who are not already
familiar with the Machinery Directive.
Regards
Nick.
At 6:21 pm +0100 19/4/06, John Woodgate wrote:
>In message <p06230916c06c146a6ccd@[192.168.1.62]>, dated Wed, 19 Apr
>2006, Nick Williams <[email protected]> writes
>>I do not agree. This approach may work for the LVD but it will
>>rapidly lead to a dead end when applied to equipment within the
>>scope of the Machinery Directive.
>
>Well, I was surprised to read what you wrote, because it's regularly
spot-on.
<SNIP>
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